We tested Collabora and its un-usable. It's terribly slow as it's basically vnc of libreoffice. It thefore requires insane spec server for use such as disroot, specially that unlike onlyoffice most of the heavy lifting is done on server side. We have tested it in the past (about half a year ago) and the results were terrible.
We do keep an eye on development and check the performance of it every now and then, but really it's nowhere near usable on deployments other then home server or small office setting.
Not sure where you get the info that most FOSS projects go collabora.